The use of multi-axis handling systems, particularly in the form of industrial robots, in conjunction with specific handling activities is e.g. known from DE 299 00 899 U1. In the case of a storage system for an article distribution centre described therein robots are used as separating devices, so that in the case of a reduced number of personnel and reduced energy use and ergonomically unfavourable ambient conditions, it is possible to ensure a time-shortened redistribution and commissioning of articles supplied in large quantities to smaller and differently packed loads or batches.
The use of industrial robots, more particularly at the end of production lines, is also known and widespread. As a rule for this purpose use is made of specific palletizing robots with four active and a fifth passive axis, where the latter is carried along by a parallelogram structure in such a way that the hand axis of the palletizing robot is always vertically oriented, i.e. the hand flange used for fixing a gripping tool is always oriented parallel to the base plane. In addition, so-called portal robots with three linear or rotary moved axes or axles are known.
The palletizing or commissioning process fundamentally takes place in accordance with a fixed diagram, no matter whether this involves the taking up of an article using a suitable gripping tool and the subsequent transportation or the setting down of the article on a pallet. The article is taken up by means of the gripping tool in a clearly defined position and usually using a conveyor and is then briefly raised by e.g. 1 to 2 cm initially with a limited speed and acceleration. This is followed by an optimum rapid movement to a position above the deposition location on a target pallet, the taking up position and the precise deposition location generally being predetermined by a specific movement algorithm, e.g. a palletizing algorithm, i.e. using corresponding software. At the end of the movement the article is slowly set down at the target location, e.g. on the pallet. The entire, above-described process can take place with multiple or single grip and is not restricted to palletizing or commissioning processes and in general terms constitutes part of numerous handling processes.
It is fundamentally desirable to operate a handling system, e.g. a robot, with maximum acceleration and speed so as to achieve very short cycle times and optimize the economic efficiency of the process. However, in general such rapid movements generally have a lateral component of motion parallel to the ground, as is particularly immediately apparent during palletizing. With a high acceleration in the lateral direction it is a consequence that correspondingly high inertia forces act on the article to be handled in the opposite direction, which in practice in the case of palletizing robots with a vertical hand axis gives rise to significant problems.
The inertia forces generally act in the centre of gravity of the article moved, whereas the holding or accelerating forces resulting from the gripping tool, which is generally constructed as a suction and/or clamping gripper and maintains the article substantially on its top surface, correspondingly act in an area outside the centre of gravity of the article moved. The occurrence of such a force couple, holding and accelerating forces on the one hand and inertia forces on the other, gives rise to a torque perpendicular to the movement direction, so that on its front side with respect to the movement direction the article is subject to a force acting downwards in addition to the weight, i.e. generally away from the gripping tool.
Where the greatest tensile forces occur between the gripping tool and the article, i.e. directly at the leading edge, the maximum tearing off or away risk occurs if the superimposing forces (weight of the article and downwardly directed tensile force through the torque resulting from acceleration and inertia) become greater than the holding force of the gripping tool. It is sufficient for this state to arise solely on one edge of the gripping tool in order to completely lose the article. This behaviour is even more critical if the article, which is generally a parallelepipedic body, is accelerated in the direction of the article surface diagonals.
In the case of single type palletizing, e.g. at the end of production lines, assistance can be provided in that on the sides of the gripping tool there is a provision of additional flaps, e.g. with cylinders operated pneumatically, which additionally retain the article counter to the action of harmful force and moment effects.
On commissioning, i.e. in the case of mixed type palletizing, this principle does not apply, because here for pallet stability reasons the palletizing process begins at the pallet sides. In the case of pallet instability this ensures that the pallet load always slides towards the middle of the pallet and not towards the outside. However, such a procedure also leads to individual articles subsequently having to be buried in in part narrow “gaps” on the pallet. However, the gripping tool must not project over the edges of the article, so that known commissioning methods can only be performed with a limited displacement speed in order to as far as possible prevent the loss of articles.
DE 44 41 240 C1 discloses a method and an apparatus with the aid of which a movement of an article on a preprogrammed path or track is made possible. This is brought about in that a compensating unit constantly initiates a system-characterizing motion equation and a compensation quantity is determined, which directly acts in the form of a control variable on the system. This permits a more precise and faster movement of the article along the predetermined path. As a result the movement of articles on a programmed path takes place without jerks and rapidly. However, it is a disadvantage of such an article movement control that no provisions are made for optimizing the path behaviour with respect to a uniform force distribution of a connection between the gripping tool and the article moved. DE 44 41 240 C1 is admittedly directed at achieving the greatest possible force-free movement of an article, but factors out the fundamentally necessary acceleration phases at the start and finish of the movement, which are particularly problematical when using industrial robots for moving articles.
Whilst avoiding the aforementioned disadvantages, the problem of the invention is to provide a method and an apparatus making it possible with simple design means to time-shorten the handling process associated with the movement of articles, particularly during palletizing or commissioning, whilst providing a maximum transportation safety with respect to the articles moved.